The invention is in the field of based light bulbs having one or more filaments accurately positioned with respect to the base.
Light bulbs for certain uses require accurate positioning and alignment of their filament (or filaments) with respect to the base. For example, replaceable light bulbs for reflector lamps such as automobile headlamps are attached at their bases to the reflector, and the bulb's filament (or filaments) must be accurately positioned or centered at or with respect to the focal point of the reflector in order that the intended light beam pattern will be produced. Certain slide and movie projectors are further examples of optical equipment requiring accurate positioning of a lamp's filament with respect to its base.
Several ways have been devised for accurately positioning a light bulb's filament (or filaments) with respect to its base. For example, U.S. Pat. No. 3,885,149 to Wolfe discloses a prefocus lamp having a light bulb secured to a capping box which is held by a cup which is held by a cylindrical sleeve to which a focusing collar is attached in accurate alignment with the filament. U.S. Pat. No. 3,469,140 to Bottone discloses a light bulb cemented into a base and adjusted to align the filament with respect to the base while the cement is soft, and held in this position until the cement hardens. U.S. Pat. Nos. 3,904,909 and 3,960,278 to Vause disclose a lamp having metal brackets partially embedded in the bulb's pinch seal and in accurate alignment with the bulb's filament.
These prior base arrangements have various undesirable characteristics such as an expensive complexity of parts and/or requiring cement or metal parts adhered to the light bulb which, due to the high temperature when the lamp is operating (especially for halide lamps), can cause the bulb to crack. The range of choice for metals and cement adhesives in contact with the bulb is thus undesirably limited to those having thermal expansion coefficients similar to that of the bulb, and the adhesives are further limited to some generally expensive high-temperature types that usually require a relatively long time to harden, thus increasing the manufacturing cost.